This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 11-150460, filed May 28, 1999; and No. 11-150461, filed May 28, 1999, the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical-electric printed wiring board having both optical interconnects and electric interconnects, a method of fabricating the same, and a printed circuit board fabricated by mounting an optical part or an electric part on the optical-electric printed wiring board.
2. Description of the Related Art
Recently, the degree of integration of transistors is increasing, among other electric elements such as semiconductor large-scale integrated circuits (LSIs). Some transistors have an operating speed of 1 GHz as a clock frequency.
To mount these highly integrated electric elements on an electric printed wiring board, packages such as a BGA (Ball Grid Array) and a CSP (Chip Size Package) have been developed and put into practical use.
Generally, as the internal clock frequency of electric elements rises, the external inter-element signal speed of these electric element rises. This high-speed, inter-element signal produces noise such as reflection caused by poor shapes of electric interconnects connecting the elements, or the influence of crosstalk. In addition, the high-speed inter-element signal generates many electromagnetic waves from the electric interconnects to adversely affect peripheral circuits. Therefore, present systems are constructed by lowering this signal speed between electric elements to the extent at which no such problems arise. In this case, however, the functions of highly integrated electric elements are not fully utilized.
To solve these problems, copper electric interconnects on a printed circuit board are partially replaced with optical interconnects such as optical fibers or optical waveguides, and optical signals are used in place of electrical signals. This is because optical signals can suppress the generation of noise and electromagnetic waves.
From the viewpoint of high-density mounting and miniaturization, it is desirable to fabricate an optical-electric printed wiring board by stacking electric interconnects and optical interconnects on the same substrate. However, when an optical part such as a laser light emitting element or light receiving element is to be mounted on a conventional optical-electric printed wiring board, it is difficult to optically align the optical axis of this optical part with that of an optical interconnect. Generally, only a skilled operator can align these optical axes. Accordingly, compared to electric parts which can be automatically soldered by a reflow furnace or the like, mounting optical parts on an optical-electric printed wiring board is very expensive.
The present invention has been made in consideration of the above drawbacks of the prior art, and has as its object to provide an optical-electric printed wiring board which can realize high-density mounting or miniaturization, and which can mount an optical part and an electric part with high accuracy, to provide a method of fabricating the same, and to provide a printed circuit board mounting an optical part or an electric part on the optical-electric printed wiring board.
One aspect of the present invention is an optical-electric printed wiring board comprising an electric wiring substrate having an electric interconnect, and an optical wiring layer stacked on the electric wiring substrate and having a surface on which an optical part is mounted, characterized in that the optical wiring layer comprises a core for propagating light, a clad for sandwiching the core, and a mirror for reflecting light propagating in the core toward the optical part, or reflecting light from the optical part into the core, and the electric wiring substrate comprises conductive setting means which is a conductor column extending through the optical wiring layer in the direction of stacking and having an end face on which the optical part to be mounted is set, the conductive setting means obtaining electrical conduction between the optical part to be mounted and the electric interconnect.
Another aspect of the present invention is a printed circuit board fabricated by mounting an optical part or an electric part on the optical-electric printed wiring board described above.
Still another aspect of the present invention is a method of fabricating an optical-electric printed wiring board, characterized by comprising the steps of forming conductive setting means on a predetermined electric interconnect of an electric wiring substrate, coating the electric wiring substrate with a first cladding layer, coating the first cladding layer with a core layer, coating a portion of the first cladding layer and the core layer with a second cladding layer to obtain an optical wiring layer, exposing an end face of the conductive setting means from the optical wiring layer, forming an electric interconnect on the optical wiring layer, and forming a mirror in a predetermined position of the optical wiring layer by perforation.
With the arrangements as described above, it is possible to provide an optical-electric printed wiring board which can realize high-density mounting or miniaturization, and which can mount an optical part and an electric part with high accuracy, to provide a method of fabricating the same, and to provide a printed circuit board fabricated by mounting an optical part or an electric part on the optical-electric printed wiring board.
Note that embodiments according to the present invention include inventions in various stages, and diverse inventions can be extracted by proper combinations of a plurality of constituent features disclosed. For example, if an invention is extracted by omitting some constituent features from all constituent features described in the embodiments, the extracted invention is carried out by properly compensating for the omitted portions by well-known conventional techniques.